There is an unfortunate tendency to talk of improvisation in jazz as a "pure" act of spontaneous creation, of playing something unlike you'd ever played before in your life. Not so. Every skilled improvisor has practiced and practiced and practiced some more. They're got a repertoire of licks and tactics that they draw on while playing a solo. It's better to think of a continuum between pure composition, which always has room for interpretive license, and pure improvisation, which never actually happens.
In this clip we see six very different musicians improvise against the same backing track. Each tells us something about the process they went through to prepare. Some prepared more extensively than others. Each is somewhere on that continuum between pure improv and deliberate composition. It would be interesting to hear each pianist play another chorus a week later, but without any extra preparation. Would there be any similarities between that chorus and the one in the video?
Each of these musicians has a channel on YouTube; they're listed in the notes at YouTube.
